In many different types of electronic equipment, electrical interconnection of two or more circuit boards is accomplished by a device known as a backplane. A typical backplane is comprised of a substrate having a plurality of rows of selectively interconnected, electrically conductive pins extending normally from one of its major surfaces. One or more of the rows of pins are each received in a separate edge connector, each carried by, and electrically connected to a separate circuit board.
Each edge connector is comprised of an insulative housing secured to a major surface of the circuit board proximate an edge thereof. The housing typically has at least one and usually several rows of spaced apertures extending therethrough, the rows of apertures being stacked one above the other in spaced relationship so that each row is parallel to the plane of the board. The apertures in each row are sized to receive a corresponding one of the pins in a row projecting from the backplane.
Extending into each aperture in the edge connector housing is a first end of an electrical contact which makes a mechanical and electrical connection with the backplane pin received in the aperture. Each contact has a second, opposite end which extends from the housing towards one of the major surfaces of the circuit board. The second end of each contact is provided with an arcuate tip or "toe" for bearing against, and making an electrical connection with, a separate one of a plurality of metallized pads on the circuit board, each pad connected to one or more components on the board. Typically, the toes, as well as the metallized pads on the board contiguous therewith, are arranged in one or more rows which are successively spaced from the edge connector housing. As may be appreciated, the metallized pads on each circuit board are selectively interconnected to the metallized pads on one or more other circuit boards via the edge connector contacts and the backplane pins.
To assure that the electrical connection between each toe and each metallized pad remains sold, the toes are soldered to the metallized pads. In the past, soldering of the toes to the pads has been done manually. However, manually soldering the toes of the edge connector contacts to the metallized pads on the boards has become increasingly more time-consuming because of an increase in the number of toes as well as a reduction in the lateral spacing therebetween. The increase in the number of edge connector toes and the reduction in the spacing therebetween has resulted from the trend in the electronics industry towards a greater density of components on a given size circuit board. This has led to a corresponding need to increase the number of connections that must be made to the circuit board by the edge connector without a corresponding increase in the size thereof.
Recently, efforts have been made at automating the process of soldering the toes of the edge connector contacts to the metallized pads on the circuit board. One approach has been to provide a convective reflow soldering apparatus for this purpose as disclosed in the article "Assembly of Bellpac.RTM. Connectors to Printed Wiring Boards" by Herbert A. Pohl, published in The Western Electric Engineer, Third Issue, Vol 47, No. 3, at pages 30-35. The Pohl soldering apparatus comprises a conveyor for transporting the circuit board past a set of heaters which direct hot air at the region where the toes of the edge connector contacts are contiguous with the metallized pads on the circuit board. A solder feeding mechanism is located downstream of the heaters for feeding solder into the region previously warned by the heaters. When the solder contacts the toe or the metallized pad contiguous therewith, the solder reflows and forms a bond between the toe and the metallized pad.
The soldering apparatus of Pohl is only useful for soldering those edge connectors having but a single row of toes, each contiguous with a separate one of a set of metallized pads lying in a single row on the circuit board. The Pohl soldering apparatus is not useful for soldering those edge connectors whose toes lie in two or more rows spaced successive distances from the edge connector housing. This is because the Pohl apparatus is generally not able to feed solder towards more than one row of toes on the edge connector at a time. Thus, during a single pass of the circuit board past the solder feeding mechanism on the Pohl apparatus, the toes lying in more than one of the rows will likely not be soldered to the corresponding metallized pads on the circuit board.
Therefore, there is a need for a technique for automated soldering of each of a plurality of edge connector toes, arranged in one or more rows, to a corresponding one of a plurality of metallized pads, arranged in a like number of rows on a circuit board.